Zirkzi’s VS Mana Sphere

Does anyone know what are the advantages of using Zirkzi’s over Mana Sphere? I don’t know how instances of damage work, but if you DoT someone with Mana Sphere, is the innate True Magic Damage also applied on the DoT? If so, I don’t see a point of using Zirkzi’s, because the rolls you can get. Mana Sphere overall gives better stats.

Demon’s Glee + Mana Sphere fighter is very popular, and I thought about why I haven’t seen any Demon’s Glee + Zirkzi’s fighter, and I think it makes sense. There’s no damage being applied over time, so the 2 True Damage from Zirkzi’s will only be applied to the inital hit from Demon’s Glee. Mana Sphere also has 2 True Magic Damage rolled innately on the item, so the 2 True Damage is the same, but Mana Sphere has better overall stats compared to Zirkzi’s.

Sorry if this is a jumble of a post, just trying to figure out why one would use Zirkzi’s over Mana Sphere, besides the Drip.